I saw.

I generated a data file based up on the information the OP gave me in response to my question. 30GB/160million records = ave. 200 bytes/record. So I used:

perl -E"printf qq[%010u,%0200u\n], $_, $_ for 1..160e6" >30GB.dat
[download]

Which makes for easy verification that the record found matches the record searched for:

E:\>head -2 s:30GB.dat
0000000001,00000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000
+000001
0000000002,00000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000
+000002

E:\>tail -2 s:30GB.dat
0159999999,00000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000159
+999999
0160000000,00000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000160
+000000
[download]

But I forgot to subtract the size of the record number, delimiter and EOL from the length of the data, so my 30GB.dat is actually 32GB:

E:\>dir s:30GB.*
28/02/2015  08:21    34,560,000,000 30GB.dat
28/02/2015  09:44     1,920,000,000 30GB.idx
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So, whilst my data does not match his, the difference doesn't affect the indexing or the timing.